Q. Is the UK gone - or will they vote again like Ireland in two recent EU referendums?

A. Yes, they are gone. No, there won't be a second vote. Technically this referendum was 'consultative' and 'non-binding'. Political reality and the history of this most explosive topic means the result cannot be ignored. But how and when the United Kingdom exit happens will take time to unfold. The Brexit terms and any new relationship with the EU will involve complex negotiations and require the agreement of the remaining 27 member states.

Q. What rules govern the UK's Brexit process?

A. The EU was like the Hotel California until 2009 - no one could ever leave. Then Article 50 of the EU Treaty was enacted as part of the Lisbon Treaty, approved after Ireland's second vote in 2009. Once Article 50 is invoked a two-year negotiating timeframe is envisaged.

Extension of the two-year talks term requires unanimous agreement of the remaining 27 member states. Failure to get unanimous agreement would mean the exit would happen automatically.

Q. Does that mean the UK will be out of the EU by summer 2018?

A. Most unlikely. Everyone involved guesses it will take more than two years to untangle 43 years of shared EU laws and regulations. There is some suggestion that Britain should begin by declaring in advance that they will need an extension.

The result was barely hours old when the first row broke out about when exactly Britain will trigger the Article 50 process.

EU Commission President Jean Claude Juncker said it should happen as soon as possible to avoid continued uncertainty. That tension will continue. Britain may get some time - but not too much.

Q. What does this famous 'exit Article 50' say?

A. In practice it gives big power to the remaining 27 member states who must agree UK Brexit terms by a so-called 'super qualified majority'. That is 72% of the remaining member countries, representing 65% of the remaining EU population.

The European Parliament must also approve any deal.

Q. Does Brexit mean passport controls and customs checks at the border being wheeled out again?

A. That is many people's worst nightmare. Both London and Dublin will work hard to avoid any return of the border. But the 300-mile stretch from Londonderry to Dundalk becomes an EU external frontier. Immigration was a big referendum campaign issue and questions about identity checks must be faced.

David Cameron said the sea - rather than the Border - might be the frontier.

The outcome, in which Northern Ireland's voters opted for Remain, has fuelled tensions.

Q. So, what kind of exit terms could the UK expect?

A. Right now, the only ones who could answer that one are a handful of people like German Chancellor Angela Merkel and French President Francois Hollande. There are arguments for making a smart and reasonably generous association deal with Britain.

Q. Can the European Union survive this shock?

A. Beware the 'domino effect'. The departure of the world's fifth largest economy from the EU comes at a time when it is at a very low ebb. Anti-EU sentiment is running high in many countries.